Essential/precursor chemical control research: Giommoni's review, understanding multi-replication interrupted time series analysis, and next steps

Controls on essential/precursor chemicals from commercial companies have been associated with many large downturns in illicit drug markets and attendant problems. My colleagues and I brought this to light in the studies that are the subject of Giommoni's review. McKetin et al. in an earlier review considered several of our studies on chemical controls for methamphetamine, all centered in North America. Giommoni discusses not only those studies but also our later work on chemical controls for cocaine and heroin. This later work evaluates US essential/precursor chemical policies targeting illicit drug producers outside of North America, and it examines impacts on illicit drug availability and use (the studies reviewed by McKetin et al. predominantly focused on outcomes such as drug-related hospitalizations, arrests, and treatment). Giommoni's review is a new resource that will help make the varied topics in essential/precursor chemical control research more accessible to many readers. After noting this, I discuss some common methodological misconceptions about our studies. For example, our studies generally used multi-replication interrupted time series analysis, a research design among the most powerful of all quasi-experimental designs. Authors, however, typically discuss the studies as if they used single-intervention interrupted time series analysis, a less powerful design. Multi-replication and single-intervention interrupted time series analyses also differ regarding likely confounders; awareness of this is critical to accurately assessing our findings and critiquing alternative explanations. Finally, I note that commercial chemical companies function as the silent, albeit usually unwitting, partners in the large-scale production of several illicit drugs, including fentanyl. And many governments are implementing essential/precursor chemical controls to help stymie this partnership. But they are doing so largely without evaluation and study—a poor policy practice. To remedy this, I suggest establishing multi-disciplinary applied research teams to help assess, guide and improve essential/precursor chemical control efforts.